Exposure apparatus

ABSTRACT

An exposure apparatus includes an illumination optical system that includes an optical integrator for forming a secondary light source from the light, and a variable stop arranged at or near a position where the secondary light source is formed, the diameter variable stop that defines a NA of the illumination optical system, a projection optical system that includes an aperture stop arranged at a position substantially optically conjugate with the variable stop, the aperture stop defining a numerical aperture of the projection optical system, and a controller for controlling the aperture diameter of the variable stop as the aperture diameter varies so that an image of the secondary light source can fall within the aperture diameter of the aperture stop.

This application is a continuation of prior application Ser. No.11/552,958, filed Oct. 25, 2006, which is a continuation of priorapplication Ser. No. 10/859,754, filed Jun. 3, 2004 and issued as U.S.Pat. No. 7,142,283 on Nov. 28, 2006, both of which are herebyincorporated by reference herein in their entirety as if fully set forthherein. This application claims the right of priority under 35 U.S.C. §119 based on Japanese Patent Application No. 2003-162044, filed on Jun.6, 2003, which is also hereby incorporated by reference herein in itsentirety as if fully set forth herein.

BACKGROUND OF THE INVENTION

The present invention relates generally to an exposure apparatus, andmore particularly to an exposure apparatus used to expose objects, suchas single crystal substrates for semiconductor wafers and glass platesfor liquid crystal displays (“LCD”).

A reduction projection exposure apparatus has been conventionallyemployed that uses a projection optical system to project or transfer acircuit pattern on a reticle (or a mask) onto a wafer, etc., in order tomanufacture fine semiconductor devices such as a semiconductor memory ora logic circuit in photolithography technology.

Recent demands for smaller and thinner profile electronic devices haveincreasingly called for finer semiconductor devices to be mounted ontothese electronic devices. The exposure apparatus is required to havesuch high optical performance as the critical dimension (or resolution)on a wafer surface of 0.2 μm or, preferably, 0.1 μm.

The semiconductor industry has recently shifted its production to ahighly value-added system chip that mixes a wide variety of patterns thereticles needing plural types of patterns. Reticle patterns include anadjacent and periodic line and space (L & S) pattern, a line of contactholes that are adjacent and periodic (i.e., arranged at the sameinterval as the holes diameters), isolated contact holes that arenon-adjacent and isolated, other isolated patterns, etc. A transfer of apattern with high resolution requires a selection of optimal exposureconditions in accordance with these kinds of patterns.

In order to handle exposure processes of various featured patterns, morespecifically, to set an exposure condition suitable for each exposureprocess, an exposure apparatus has been proposed (for example, inJapanese Patent Application, Publication No. 5-299321) that can change anumerical aperture (“NA”) in the projection optical system, anillumination condition, such as a coherence factor σ (i.e., a ratio ofan illumination optical system's NA to a projection optical system'sNA), and a σ distribution in the illumination area (for a so-calledmodified illumination, such as an oblique incidence illumination, amulti-pole illumination, and an off-axis illumination).

However, when the projection optical system's NA, the illuminationoptical system's NA and an effective light source shape are changedindependently, the illumination light from the illumination opticalsystem can be larger than the projection optical system's NA anddisadvantageously shielded by the projection optical system. As aresult, the imaging performance deteriorates and the light intensitybecomes uneven. In particular, the recently frequently used modifiedillumination among the resolution-enhanced technology (“RET”) has alarge σ value, thus this problem is likely to happen.

The exposure apparatus proposed in the above reference includes a meansfor alarming an error or prohibiting an exposure action when anoperator's setting causes the 0-th order light in illumination light,that passes through an illumination stop and the reticle, not to passthrough the projection optical system. Thus, this reference arduouslyrequires the operator to avoid this problem at the time of the setting.

In addition, as the off-axis telecentricity is adjusted for correctionsof on-axis and off-axis telecentricity, the outline of the σdistribution decenters, the projection optical system can similarlyshield the illumination light, and the imaging performance deteriorates.It is therefore important that the illumination light (in particular,the 0-th order light) enters the projection optical system in view ofits NA even when the σ distribution decenters.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is an exemplified object of the present invention toprovide an exposure apparatus that prevents shielding of theillumination light and provides excellent imaging performance.

An exposure apparatus of one aspect according to the present inventionincludes an illumination optical system for illuminating a reticle usinglight from a light source, wherein the illumination optical systemincludes an optical integrator for forming a secondary light source fromthe light, and a variable stop arranged at or near a position where thesecondary light source is formed, the variable stop being configured tovary an aperture diameter that defines a numerical aperture of theillumination optical system, a projection optical system for projectinga pattern on the reticle onto an object to be exposed, wherein theprojection optical system includes an aperture stop arranged at aposition substantially optically conjugate with the variable stop, theaperture stop defining a numerical aperture of the projection opticalsystem, and a controller for controlling the aperture diameter of thevariable stop in the illumination optical system as the aperturediameter of the variable stop varies so that an image of the secondarylight source formed at or near the aperture stop can fall within theaperture diameter of the aperture stop.

An illumination apparatus of another aspect according to the presentinvention for illuminating a surface using light from a light sourceincludes a condenser optical system that includes at least two groups ofoptical systems for introducing the light into the surface, wherein thecondenser optical system makes a focal length and a back principal pointposition of the condenser optical system substantially constant, whilemaking a front principal point position of the condenser optical systemvariable.

An illumination apparatus of still another aspect according to thepresent invention for illuminating a surface using light from a lightsource includes an optical integrator for forming a secondary lightsource from the light, and a condenser optical system that introducesthe light from the optical integrator into the surface, and includes atleast two groups of optical systems, wherein the condenser opticalsystem makes a focal length and a back principal point position of thecondenser optical system substantially constant, while making a frontprincipal point position of the condenser optical system variable.

An illumination apparatus of still another aspect according to thepresent invention for illuminating a surface using light from a lightsource includes a zooming optical system for introducing the light to anoptical integrator and for adjusting a size of a secondary light sourceformed by the optical integrator, and a condenser optical system thatintroduces the light from the optical integrator to the surface to beilluminated, and includes at least two or more optical elements, whereinthe zooming optical system adjusts the size of the secondary lightsource in accordance with an adjustment of an interval between theoptical elements that constitute the condenser optical system.

An exposure apparatus of another aspect according to the presentinvention includes the above illumination optical system, and aprojection optical system for projecting a pattern on a reticleilluminated by the illumination optical system, onto an object to beexposed.

A device fabricating method of still another aspect of the presentinvention includes the steps of exposing an object using the aboveexposure apparatus, and performing a predetermined process for theexposed object. Claims for a device fabricating method that performsoperations similar to that of the above exposure apparatus cover devicesas intermediate and final products. Such devices include semiconductorchips like an LSI and VLSI, CCDs, LCDs, magnetic sensors, thin filmmagnetic heads, and the like.

Other objects and further features of the present invention will becomereadily apparent from the following description of the preferredembodiments with reference to accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural view of an exposure apparatus of oneembodiment according to the present invention.

FIG. 2 is a schematic view showing an exemplary relationship between thelight intensity distribution on the incident surface and that on theexist surface of a fly-eye lens shown in FIG. 1.

FIG. 3 is an enlarged view of a principal part in an illuminationoptical system in the exposure apparatus shown in FIG. 1.

FIG. 4 is a schematic sectional view of a ray shape in a variable stopin the illumination optical system shown in FIG. 1.

FIG. 5A to 5C are schematic plane views of various aperture stopsapplicable to the shaping means shown in FIG. 1.

FIG. 6 is a schematic view showing a relationship between the lightincident upon the fly-eye lens shown in FIG. 1 and the illuminatedsurface.

FIG. 7 schematically shows effective light source distributions atrespective image points on the illuminated surface when a ray having thelight intensity distribution shown in FIG. 2 enters the fly-eye lensshown in FIG. 1.

FIG. 8 schematically shows effective light-source distributions atrespective image points on the illuminated surface when a ray having thelight intensity distribution shown in FIG. 2 enters the fly-eye lensshown in FIG. 1 and the telecentricity of the effective light sourcedistribution is corrected.

FIG. 9 is a schematic view of an image of a variable stop in theillumination optical system on the aperture stop in the projectionoptical system shown in FIG. 1.

FIG. 10 is an enlarged view of a principal part of the illuminationoptical system in the exposure apparatus shown in FIG. 1.

FIG. 11 is a flowchart of an exposure method according to one aspect ofthe present invention.

FIG. 12 is a flowchart for explaining how to fabricate devices (likesemiconductor chips such as ICs and LCDs, CCDs, and the like).

FIG. 13 is a detailed flowchart of the wafer process shown in Step 4 ofFIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, a description will be givenof an exposure apparatus 1 according to the present invention. Eachelement in each figure is designated by the same reference numeral, anda duplicate description will be omitted. FIG. 1 is a schematicstructural view of the exposure apparatus 1. The exposure apparatus 1includes, as shown in FIG. 1, an illumination apparatus 100, a reticle200, a projection optical system 300, a plate 400, and a controller 500.The exposure apparatus 1 is a projection exposure apparatus that exposesonto the plate 500 a circuit pattern created on the reticle 200, forexample, by a step-and-repeat or by a step-and-scan manner.

The illumination apparatus 100 illuminates the reticle 200, and includesa light source section 110 and an illumination optical system 120.

The light source section 110 employs, for example, lasers such as an ArFexcimer laser with a wavelength of approximately 193 nm, or a KrFexcimer laser with a wavelength of approximately 248 nm, etc., but thetype of laser is not limited to an excimer laser, and an F₂ excimerlaser with a wavelength of approximately 157 nm can be used. The numberof light sources is also not limited. When the light source section 110uses a laser, it is desirable to employ a beam shaping optical systemthat shapes a parallel beam from a laser source to a desired beam shape,and an incoherently turning optical system that turns a coherent laserbeam into an incoherent one. A light source applicable to the lightsource section 110 is not limited to the laser, but may use one or morelamps such as a mercury lamp, xenon lamp, etc.

The illumination optical system 120 is an optical system forilluminating the reticle 200, and includes a lens, a mirror, an opticalintegrator, a stop, etc. The illumination optical system of the instantembodiment includes a uniform ray forming means 121, a shaping means122, a zooming (or imaging) optical system 123 a to 123 c, a fly-eyelens 124, a variable stop 125, a condenser optical system 126, a maskingblade 127, and imaging optical systems 128 and 128 b. A detaileddescription of the illumination optical system will be given later.

The reticle 200 is made from quartz, for example, and forms a circuitpattern (or an image) to be transferred, and is supported and driven bya reticle stage (not shown). Diffracted light emitted from the reticle200 passes through the projection optical system 300, and then isprojected onto the plate 400. The reticle 200 and the plate 400 arelocated in an optically conjugate relationship. The exposure apparatus 1of the instant embodiment is a scanner, and the reticle 200 and theplate 400 are scanned at a speed ratio corresponding to a reductionratio to transfer the pattern on the reticle 200 onto the plate 400. Ifit is a step-and-repeat exposure apparatus (referred to as a “stepper”),the reticle 200 and the plate 400 remain still for the exposure.

The projection optical system 300 is an optical system for projectinglight that reflects the pattern on the reticle 200 onto the plate 400.The projection optical system 300 has an aperture stop 310 that definesan arbitrary NA. The aperture stop 310 has a variable aperture diameterthat defines the NA of an imaging ray on the plate 400, and varies theaperture diameter to adjust the NA if necessary. In the instantembodiment, σ is a ratio between the diameter of an image of each lightsource formed by a fly-eye lens 124 at a position of the aperture stop310 and the aperture diameter of the aperture stop 310.

The projection optical system 300 of the instant embodiment is anoptical system that includes only plural lens elements 320 a and 320 b,but may also be a catadioptric optical system comprised of a pluralityof lens elements with at least one concave mirror, an optical systemcomprised of a plurality of lens elements and at least one diffractionoptical element such as a kinoform, a catoptric optical system includingonly mirrors, and so on. Any necessary correction of a chromaticaberration in the projection optical system 300 can use a plurality oflens units made from glass materials having different dispersion values(Abbe values), or arrange a diffraction optical element such that itdisperses in a direction opposite to that of the lens unit.

The plate 400 is a wafer in the instant embodiment, but may include aliquid crystal plate and a wide range of other objects to be exposed. Aphotoresist is applied onto the plate 400.

The plate 400 is supported by the plate stage 450. The plate stage 450may use any structure known in the art, and a detailed description ofits structure and operations is omitted. For example, the plate stage450 uses a linear motor to move the plate 400 in X-Y directions. Thereticle 200 and plate 400 are, for example, scanned synchronously, andthe positions of the reticle stage (not shown) and plate stage 450 aremonitored, for example, by a laser interferometer and the like, so thatboth are driven at a constant speed ratio. The plate stage 450 isinstalled on a surface plate stool supported on the floor and the like,for example, via a dumper, while the reticle stage (not shown) and theprojection optical system 300 are installed on a barrel surface (notshown) supported by the base frame placed on the floor, for example, viaa dumper.

The controller 500 includes a CPU (not shown) and a memory (not shown),and controls the actions of the exposure apparatus 1. The controller 500is electrically connected to the illumination apparatus 100, the reticlestage (not shown), the projection optical system 300, and the platestage 450. The controller 500 controls the aperture diameter of avariable stop 125 in the illumination optical system 120 so that animage from the secondary light source, formed by the fly-eye lens 124 ata position of the aperture stop 310 in the projection optical system300, falls within the aperture diameter of the aperture stop 310. Thecontroller 500 controls the aperture diameter of the variable stop 125in the illumination optical system 120 so that σ≦(x−1)/x where x is thenumber of fine lenses in the fly-eye lens 124 corresponding to σ=1. Thefly-eye lens 124 serves as an optical integrator and generally includestwenty or more optical elements (such as fine lenses). The controller500 controls the ratio between the illumination optical system 120's NAand the projection optical system 300's NA so that (the illuminationoptical system 120's NA)/(the projection optical system 300's NA) isless than or equal to, for example, 0.95. The controller 500 may serveas an adjuster 600, which will be described later.

A description will now be given of the illumination optical system 120,with reference to FIGS. 2 to 10. The light emitted from the light sourcesection 110 that has an excimer laser, etc., is converted into anapproximately uniform light distribution on a predetermined surface A bya uniform ray forming means 121. The uniform ray forming means 121includes at least one of the following: a fly-eye lens, an optical pipethat uses internal reflections, a diffraction grating, etc., or acombination thereof, such as a plurality of optical integrators, a relayoptical system, a condenser optical system, a mirror, etc. The uniformray forming means 121 varies light from the light source section 110into a desired uniform light distribution on the predetermined surfaceA. The predetermined surface A may arrange a stop having a circular oroctagonal shape to limit the light distribution into a XY symmetricaldistribution.

A shaping means 122 makes the center part of the secondary light sourceformed by the fly-eye lens darker than the peripheral part, and isremovably located near the predetermined surface A.

The shaping means 122 can use a conical optical element 122 a, aninterval variable conical optical element 122 b, a properly shaped stop,such as a quadrupole aperture stop 122 c shown in FIG. 5A, a dipoleaperture stop 122 d shown in FIG. 5B, and an annular aperture stop 122 eshown in FIG. 5C, a parallel plate (not shown), a pyramidal opticalelement (not shown), a triangle pole shaped optical element (not shown),a variable stop that can change a shape and/or a diameter, a filterhaving a proper transmittance distribution, or a modification-variableenlargement/reduction beam expander.

The shaping means 122 can arrange some of these elements on the opticalaxis at the same time.

The conical optical element 122 a has a concave conical incidentsurface, and a convex conical exit surface, and serves to form anannular ray when located along the optical axis.

The conical optical element 122 b includes an optical element OM₁ thathas a concave conical incident surface and a flat exit surface, and apyramidal optical element OM₂ that has a flat incident surface and aconvex conical exit surface. The conical optical element 122 b whenlocated along the optical axis forms an annular ray. The adjusting of aninterval between the optical elements OM₁ and OM₂ can change the size ofthe annulus (or an annular ratio). Such a structure of the conicaloptical element 122 b can efficiently form the annular ray in a smallspace. The optical elements OM₁ and OM₂ have approximately the sameconical surface angle. The same angle would reduce the angle of the exitlight from the shaping means 122, and minimize the shielding of light bythe subsequent optical systems. When the subsequent optical system hasangular latitude, these angles are not necessarily made the same, butmay be different, for example, in order to reduce an annular width.

Similar to the conical optical element 122 b, is an interval variablequadrupole conversion element that has an incident side optical elementwith a concave pyramidal incident surface and an exit side opticalelement with a convex pyramidal surface. A triangle pole shaped, dipoleconversion element is also applicable. The shaping means 122 uses such aproper transmission optical element and can convert a ray shape into onein which the peripheral part has a larger light intensity distributionthan that of the central part.

FIG. 5A is a schematic plane view of the quadrupole aperture stop 122 cthat has a light shielding part LT, and quadrupole light transmittingparts TM, each having a circular opening with a transmittance of 1. Thetransmitting parts TM are arranged at ±45° and ±135°. Preferably, eachtransmitting part TM provides the same σ to the illumination light. Thetransmitting parts TM can be formed in directions of 0°, 90°, 180° and270° or have different sizes according to patterns on the reticle 200.The transmitting part TM may have such various shapes as a rectangle,another polygon, or part of a sector. FIG. 5B is a schematic sectionalview of the dipole aperture stop 122 d having a light shielding part LTand dipole light transmitting parts TM having circular openings with atransmittance of 1. FIG. 5C is a schematic plane view of an annularaperture stop 122 e having a light shielding part LT and a lighttransmitting part TM having an annular opening with a transmittance of1.

A magnification-variable zooming optical system (123 a to 123 c) variesa magnification of the circular shaped ray formed on the predeterminedsurface A or the ray that has been desirably shaped by the shaping means122. The circularly or desirably shaped ray enters the incident surfaceof the fly-eye lens 124 that serves as the optical integrator.

The fly-eye lens 124 serves as the optical integrator, and forms aplurality of light source images or secondary light sources near theexit surface of the fly-eye lens 124 from the incident light. Thevariable stop 125 is provided near the surface, on which the plurallight source images are formed. The variable stop 125 is located at aposition that slightly defocuses (by ±several millimeters) from thesurface, on which the plural light source images are formed (or a backfocal surface of the fine lenses that form the fly-eye lenses) becausethe surface has a comparatively high energy density of light. When thevariable stop 125 endures the energy density, the variable stop 125 canbe located on the surface, on which the plural light source images areformed.

The variable stop 125 can vary an aperture diameter that defines theillumination optical system 120's NA. The aperture diameter is variedaccording to the projection optical system 300's NA, as discussed later.The variable stop 125 and the aperture stop 310 are arranged in asubstantially optically conjugate relationship. The fly-eye lens 124forms multiple light sources at the exit surface side of the variablestop 125, and their images formed at the position of the aperture stop310 provide a shape of the illumination ray (or an effective lightsource shape) at respective points on the plate 400 surface. Themultiple light sources formed by the fly-eye lens 124 are not restrictedby the variable stop 125, and are referred to as “secondary lightsources” hereinafter.

Among rays from the multiple light source images, rays that are notrestricted by the variable stop 125 illuminate the masking blade 127'ssurface via the condenser optical systems 126 a and 126 b. The maskingblade 127 is arranged, via the imaging optical systems 128 a and 128 b,at a surface substantially optically conjugate with the surface wherethe reticle 200 is arranged. The masking blade 127 defines anilluminated area on the reticle 200's surface.

When the images of the secondary light sources at the aperture stop 310position in the projection optical system 300 are larger than theaperture stop 310, the direct light that has transmitted through theillumination optical system 120 (or the 0-th order light from thereticle 200) is shielded by (the light shielding part on) the aperturestop 310 in the projection optical system 300. As a result, asdiscussed, is that the imaging performance deteriorates and the lightintensity becomes uneven, negatively affecting the semiconductor devicemanufacture.

Accordingly, the inventive exposure apparatus 1 uses the controller 500to control the aperture diameter of the variable stop 125 in theillumination optical system 120 as the projection optical system 300'sNA varies, so that the 0-th order light from the reticle 200, which haspassed through the variable stop 125 in the illumination optical system120, falls within the aperture diameter in the aperture stop 310 in theprojection optical system 300. In other words, the controller 500controls the illumination optical system 120's NA so that the 0-th orderlight from the reticle 200 is not shielded by the aperture stop 310 inthe projection optical system 300.

FIG. 2 is a schematic view showing an exemplary relationship between alight intensity distribution on the incident surface and that on theexist surface of the fly-eye lens 124 shown in FIG. 1. However, strictlyspeaking, FIG. 2 exemplarily shows a relationship between a lightintensity distribution on the incident surface of the fly-eye lens 124and that of the secondary light sources formed near the variable stop125.

In FIG. 2, D₀ is an exemplary light intensity distribution on theincident surface of the fly-eye lens 124, and E is an exemplarysecondary light source.

The light source distribution of light emitted from the light sourcesection 110 is converted into a discrete distribution corresponding tothe fine lenses in the fly-eye lens 124 when the light passes throughthe fly-eye lens 124. The peak outline E₀ that connects peak values ofthe discrete distribution has approximately the same shape as that ofthe light intensity distribution D₀ for the aperture diameter of thevariable stop 125 in the illumination optical system 120. Substantially,the light intensity distribution D₀ and the aperture diameter of thevariable stop 125 determine a shape of the secondary light source.

FIG. 3 is an enlarged view of a principal part in an exemplaryillumination optical system 120 in the exposure apparatus 1 shown inFIG. 1. FIG. 4 is a schematic sectional view showing a ray shape in avariable stop 125 in the illumination optical system 120 shown in FIG.1.

FIG. 3A shows so-called normal illumination where the shaping means 122is retreated from the optical path or where a circular stop or aparallel plate is arranged near the predetermined surface A. Asillustrated, the uniform ray forming means 121 forms a substantiallycircular shaped ray with a uniform light intensity distribution on thepredetermined surface A. Due to the uniform ray forming means 121, raysfrom plural angles overlap each other and form a uniform light intensitydistribution on the predetermined surface A; even when the light sourcesection 110 uses a light source having strong directivity such as alaser, the light can maintain a certain NA as shown by an arrow in FIG.3A.

The magnification-variable zooming optical system (123 a-123 c) projectsthe light intensity distribution on the predetermined surface A onto theincident surface of the fly-eye lens 124 at a predeterminedmagnification. The light intensity distribution when imaging on theincident surface of the fly-eye lens 124 without aberration wouldexhibit a sharp outline, and causes uneven light intensity and uneveneffective light source on the screen of the plate 400 that serves as anexposed surface. Therefore, imaging between the predetermined surface Aand the incident surface of the fly-eye lens 124 preferably needsaberration (including defocusing) to some extent. This is not true whenthe fly-eye lens 124 includes many fine lenses and the influence on theuneven light intensity, etc. is small. Blurs corresponding to about oneor more fine lenses are usually preferable. FIG. 4D is a sectional viewof a light intensity distribution F4 in such a state.

As described with reference to FIG. 2, the light intensity distributionof the fly-eye lens 124 substantially determines the shape of thesecondary light source (or an effective light source). In FIG. 3A, thesecondary light source is small enough for the variable stop 125 in theillumination optical system 120. In order to change a σ value (effectiveσ value that considers the distribution), the magnification-variablezooming optical system (123 a to 123 b) varies a magnification as shownin FIG. 3B. While the instant embodiment varies the σ value by changingan interval between the optical systems 123 a and 123 b, any otherconfiguration can be available as long as the magnification becomesvariable. A zooming optical system that approximately maintains thetelecentricity at the exit side of the light is preferable when themagnification changes (so that the light incident upon the fly-eye lensdoes not exceed a certain incident angle after the magnification ischanged). When the zooming optical system (123 a-123 c) has a smallmagnification variable range, the shaping means 122 can employ the(enlargement/reduction) beam expander and a stop having a small openingdiameter. FIG. 4E shows a large σ value that forms a light intensitydistribution F₅ slightly larger than the aperture diameter in thevariable stop 125 in the illumination optical system 120, and the lightthat exceeds the aperture diameter in the variable stop 125 is shieldedas unnecessary light. Such a configuration effectively switches thenormal illumination between about σ=0.1 to about σ=0.9.

The exposure apparatus 1 allows the controller 500 to automatically varythe aperture diameter in the variable stop 125 in the illuminationoptical system 120 in accordance with the set NA in the projectionoptical system 300. The controller 500 sets the aperture diameter of thevariable stop 125 so that its mechanical size is a fixed value thatsatisfies that σ is about 0.95 or smaller for the projection opticalsystem 300's NA. Alternatively, the fixed value itself can be changed.

FIG. 3C shows the illumination optical system 120 for the annularillumination. The conical optical element 122 a and annular aperturestop 122 c convert a circular light intensity distribution formed on thepredetermined surface A into an annular shape, and the annular lightintensity distribution is projected onto the incident surface of thefly-eye lens 124 at a proper magnification for so-called annularillumination. In this case, the controller 500 automatically sets theaperture diameter of the variable stop 125 in the illumination opticalsystem 120 in accordance with the projection optical system 300's NA sothat its mechanical size is a fixed value that satisfies that σ is about0.95 or smaller.

FIG. 4A shows a relationship between the variable stop 125 in theillumination optical system 120 for the annular illumination and thesecondary light source (or effective light source). Referring to FIG.4A, the annular light intensity distribution F₁ is formed within theaperture diameter in the variable stop 125. FIG. 4B shows a sectionallight intensity distribution F₂ that is a section of the annular lightintensity distribution F₁ shown in FIG. 4A in an X direction.

In the case of the annular illumination, the sectional light intensitydistribution F₂ is usually defined as a flat distribution, as shown inFIG. 4B. However, it is difficult to effectively form the flat sectionallight intensity distribution F₂, and a pursuit of efficiency wouldresult in the sectional light intensity distribution F₃ having a unevendistribution as shown in FIG. 4C. As a result of a simulation, etc. ofthe imaging performance, the sectional light intensity distribution F₃is selected for performance purposes, which is approximately equivalentto the sectional light intensity distribution F₂ shown in FIG. 4B.

The annular illumination is often used to image fine patterns. Theeffective outer σ, which is the size outside the annular shape when theimaging performance is converted into the flat sectional light intensitydistribution F₂ shown in FIG. 4B, often uses about 0.9 for the annularillumination. In this case, as shown in FIG. 4C, the small part that islocated outside the sectional light intensity distribution F₂ has a σ of0.95 or greater, possibly deviating the light from the aperture diameterin the aperture stop 310 in the projection optical system 300.Therefore, the exposure apparatus 1 allows the controller 500 to controlthe size of the aperture diameter in the variable stop 125 in theillumination optical system 120 in accordance with the projectionoptical system 300's NA while maintaining σ to be about 0.95, andadjusting the light intensity distribution to provide the desiredannular illumination.

As discussed, the inventive exposure apparatus 1 automatically variesthe illumination optical system 120's NA according to the set NA of theprojection optical system 300, facilitating the operator'smanipulations. A stop in an illumination optical system in aconventional exposure apparatus determines an effective light source,whereas the variable stop 125 in the illumination optical system 120 issupplemental, and an optical system prior to the fly-eye lens 124substantially defines an effective light source in the inventiveexposure apparatus 1. Therefore, the aperture diameter in the variablestop 125 in the illumination optical system 120 can be uniquelydetermined according to the projection optical system 300's NA.

A description will now be given of the reason why the aperture diameterof the variable stop 125 in the illumination optical system 120 is setso that σ is less than or equal to 0.95 rather than σ=1. FIG. 6 is aschematic view showing a relationship between the light incident uponthe fly-eye lens 124 shown in FIG. 1 and an illumined surface C. Theilluminated surface C is an optically conjugate surface such as themasking blade 127 surface or the reticle 200 surface, with the surfaceof an object to be exposed (the plate 400 surface).

Rays L₁, L₂ and L₃ incident upon the center fine lens MLa among the finelenses ML that form the fly-eye lens 124 form one light source image SIdue to the fine lens MLa, and Koehler-illuminates the illuminatedsurface C via the condenser optical system 126. The light source imageSI is located at the center of the opening of the variable stop 125, andrays L₁′, L₂′ and L₃′ from the light source image SI constituteprincipal rays at respective image points C₁ to C₃. FIG. 6 shows atelecentric system on the illuminated surface C, and shows that when theeffective light source is telecentric at respective image points C₁ toC₃ on the illuminated surface C, the illumination light is telecentricon the plate 400's surface as the object surface to be expected.

The telecentricity of the plate 400's surface is an important factor forthe imaging performance. Non-telecentricity leads to an asymmetricalimage.

FIG. 7 is a schematic view of an effective light source distribution atrespective image points on the illuminated surface C when the lightintensity distribution D₀ shown in FIG. 2 enters the fly-eye lens 124shown in FIG. 1. Referring to FIG. 7, the effective light sourcedistribution D₁ at the image point C₁ on the illuminated surface C, issimilar to the position P₁ on the light intensity distribution D₀ whoseprincipal ray enters the fly-eye lens 124, and maintains thetelecentricity. The effective light-source distribution D₂ at the imagepoint C₂ at the outermost axis on the illuminated surface C is adistribution corresponding to the light intensity distribution D₀ at theposition P₂ whose principal ray enters the fly-eye lens 124. Therefore,the image point C₂ of the illuminated surface C provides the effectivelight-source distribution D₂ that has the telecentricity offset by ahalf-pitch of the fine lens MLa that forms the fly-eye lens 124.

Light that has a flat sectional light intensity distribution andilluminates an area much larger than the aperture diameter in thevariable stop 125 in the illumination optical system 120 also providesthe effective light-source distribution that has the telecentricityoffset by a half-pitch of the fine lens MLa. This is not a matterbecause the flat sectional light intensity distribution is maintainedeven when the telecentricity is offset by a half-pitch. In other words,a problem arises when light that has an unflat sectional light intensitydistribution illuminates an area smaller than the aperture diameter inthe variable stop 125 in the illumination optical system 120.

FIG. 8 schematically shows that the light having the light intensitydistribution D₀ shown in FIG. 2 enters the fly-eye lens 124 shown inFIG. 1 and the telecentricity of the effective light source distributionis corrected at each image point on the illuminated surface C. FIG. 8corrects the inclination of the principal ray (that passes through thecenter of the variable stop 125) at the image point C₂ at the outermostaxis of the illuminated surface C in order to correct the telecentricityof the illuminated surface C. Although the inclined principal ray losesthe telecentricity, a correction to maintain the telecentricity isavailable for the effective light source distribution D₂ at the imagepoint C₂.

The condenser optical system 126 has an adjuster 600 to correcttelecentricity. The adjuster 600 serves to vary an interval amongoptical elements (such as lenses) in the condenser optical system 126that includes at least two groups of optical systems, and change onlythe front principal point position of the condenser optical system 126while hardly changing the focal distance of the condenser optical system126 and the back principal point position of the condenser opticalsystem 126. In other words, when the adjuster 600 moves, in anoptical-axis direction, a position of an image of the variable stop 125in the illumination optical system 120, which is formed near theaperture stop 310 in the projection optical system 300, thetelecentricity of the effective light source is corrected at respectiveimage points. The above system can be realized, for example, by anafocal optical system that has a non-equimultiple magnification andexits approximately parallel light in response to incident parallellight that is set to a front group in the condenser optical system 126,and a position of the front group is made variable in the optical-axisdirection.

The light intensity distributions have various telecentric offsets onthe incident surface of the fly-eye lens 124, and the adjuster 600varies a principal point position of the condenser optical system 126 toprovide optimal telecentricity, and changes the effective light sourceshape.

When the focal distance of the condenser optical system 126 slightlychanges as the principal point position of the condenser optical system126 changes and the size of the effective light source on theilluminated surface C consequently changes, a fine adjustment isperformed by the magnification of the zooming optical system (123 a to123 c).

When the condenser optical system 126 and the adjuster 600 thus varyinclinations at respective image points C₁ to C₃ of light that passesthrough the center of the variable stop 125 in the illumination opticalsystem 120, an image of the variable stop 125 at the aperture stop 310position in the projection optical system 300 is formed, as shown inFIG. 9, so that an image D₁A of the light that passes through the centerof the center image point C₁ is formed at an aperture position in theaperture stop 310, and an image D₂A of the light that passes through thecenter of the image point C₂ as the outermost axis decenters from thecenter of an aperture position in the aperture stop 310. Therefore, whena diameter of the image D₁A is set to 1, relative to the aperturediameter of the aperture stop 310 in the projection optical system 300(or where the mechanical σ=1 in the variable stop 125), the image D₁Aprojects outside the aperture diameter of the aperture stop 310. Here,FIG. 9 is a schematic view of an image of the variable stop 125 in theillumination optical system 120 at the aperture stop 310 in theprojection optical system 300 shown in FIG. 1.

Other factors should be considered, such as scattering sizes anddistortions of respective image points and telecentric adjustmentmargins, the diameter of the image D₁A preferably being limited to about95% of the aperture stop 310 (or the σ of the geometric shape of thevariable stop 125 being 0.95). When the number of fine lenses is smallin the fly-eye lens 124 or when the set precision is bad, a small σ ispreferable. Here, the scattering sizes and distortions of respectiveimage points result from a decentered optical arrangement between thevariable stop 125 in the illumination optical system 120 and theaperture stop 310 in the projection optical system 300, their setprecisions, and the aberration of the optical system 126. Thetelecentric adjustment is necessitated as a result of uneven coating anderrors in the optical system.

FIG. 10 is an enlarged view of a principal part of the illuminationoptical system 120 in the exposure apparatus 1 shown in FIG. 1. Thisfigure shows an example where the variable stop 125 in the illuminationoptical system 120 is used to change the effective light sourcedistribution rather than for supplemental use. The shaping means 122(which is the conical optical element 122 a in the instant embodiment)forms a ray having a light intensity distribution with a predeterminedannular ratio (e.g., a 1/2 annulus). The zooming optical system (123 ato 123 c) then properly changes a magnification of the ray having thepredetermined annular ratio, and the ray then enters the incidentsurface of the fly-eye lens 124, forming secondary light sources havingthe predetermined annular ratio near the exit surface of the fly-eyelens 124. The outside of the light intensity distributions of themultiple light sources is appropriately restricted by changing theaperture diameter of the variable stop 125. Changes of the magnificationof the zooming optical system (123 a to 123 c) and the aperture diameterof the variable stop 125 can form an effective light source having sucha desired size as a large annular ratio (such as 2/3 and 3/4 annuluses)irrespective of the annular ratio formed by the shaping means 122.

When the shaping means 122 uses the conical optical element 122 b theannular ratio can be varied by changing the interval between the opticalelements OM₁ and OM₂. However, the fly-eye lens 124 is restricted in itsincident angle, and when the incident angle exceeds a certain angle, theray becomes unnecessary, deforms the effective light source, andgenerates uneven light intensity. Therefore, the incident angle of thelight upon the fly-eye lens 124 should be at a certain angle or smaller.

The nature of the light satisfies Ar×Ad≦Br×Bd, where Ar is the radius ofthe ray shape on the predetermined surface A, Ad is the ray's NA on thepredetermined surface A, Br is the radius of the ray on the incidentsurface of the fly-eye lens 124 or the width of an annular distribution,and Bd is the ray's NA on the incident surface of the fly-eye lens 124.Therefore, when the annular distribution has a small width Br, the ray'sNA on the incident surface on the fly-eye lens 124 can exceed theincident angle limit of the fly-eye lens 124.

Therefore, even when the shaping means 122, such as the conical opticalelement 122 b, is used, the annular ratio cannot freely be made large.Therefore, the annular ratio can be effectively changed by setting theinterval between the optical elements OM₁ and OM₂ and the magnificationof the zooming optical system (123 a to 123 c) in the above restrictedrange of the incident angle upon the fly-eye lens 124, and by changingthe aperture diameter of the variable stop 125 in the illuminationoptical system 120 to reduce the outer diameter.

This is not limited to the annular illumination, but is applicable tothe quadrupole illumination and dipole illumination. An effective lightsource having a desired shape (or a modified illumination) is formedwhen the shaping means 122 converts a ray into a desired size (one inwhich a center part has a lower light intensity distribution than thatof the peripheral part), and the variable stop 125 in the illuminationoptical system 120 restricts an outer diameter of the light intensitydistribution of a secondary light source formed on the exit surface ofthe fly-eye lens 124. Even in this case, the controller 500 controlsrelative to the set NA of the projection optical system 300 so that thevariable stop 125 in the illumination optical system 120 has a geometricσ of 0.95 or smaller.

A description will be given of an exposure method using the exposureapparatus 1 with reference to FIG. 11. FIG. 11 is a flowchart forexplaining the exposure method 1000 as one aspect according to thepresent invention.

First, an operator sets the projection optical system 300's NA accordingto the circuit pattern to be transferred onto the plate 400 (or anecessary resolution) (step 1002). The operator can arbitrarily set theprojection optical system 300's NA, and the controller 500 changes theaperture diameter of the aperture stop 310 in the projection opticalsystem 300 to adjust the projection optical system 300's NA to the setNA.

The controller 500 calculates the illumination optical system 120's NAsuitable for the set NA of the projection optical system 300 so that the0-th order light from the pattern on the reticle 200 falls within theset NA's aperture in the projection optical system 300, morespecifically, the illumination optical system 120's NA/the projectionoptical system 300's NA≦0.95 (step 1004).

Next, the illumination optical system 120's NA is changed to the NA thatwas calculated in step 1004 (step 1006). This is done by changing theaperture diameter in the variable stop 125 in the illumination opticalsystem 120 to the set illumination optical system 120's NA to a settingmost suitable for the projection optical system 300's NA.

In exposure, light emitted from the light source section 110, forexample, Koehler-illuminates the reticle 200 through the illuminationoptical system 120. The light that has passed and reflects the reticlepattern forms an image on the plate 400 through the projection opticalsystem 300. The exposure apparatus 1 appropriately sets a ratio betweenthe illumination optical system 120's NA and the projection opticalsystem 300's NA, and provides excellent devices (such as semiconductordevices, LCD devices, image pick-up devices (such as CCDs), and thinfilm magnetic heads) with high throughput and economical efficiency.Once the projection optical system 300's NA is set, the controller 500automatically sets the illumination optical system 120's NA. Therefore,the operator runs the exposure apparatus 1 more easily than aconventional one.

Referring now to FIGS. 12 and 13, a description will be given of anembodiment of a device fabricating method using the above exposureapparatus 1. FIG. 12 is a flowchart for explaining the fabrication ofdevices (i.e., semiconductor chips such as IC and LSI, LCDs, CCDs,etc.). Here, as an example, a description will be given of thefabrication of a semiconductor chip as an example. Step 1 (circuitdesign) designs a semiconductor device circuit. Step 2 (reticlefabrication) forms a reticle having a designed circuit pattern. Step 3(wafer preparation) manufactures a wafer using materials such assilicon. Step 4 (wafer process), which is referred to as a pretreatment,forms actual circuitry on the wafer through photolithography using thereticle and wafer. Step 5 (assembly), which is also referred to as aposttreatment, forms into a semiconductor chip the wafer formed in Step4 and includes an assembly step (e.g., dicing, bonding), a packagingstep (chip sealing), and the like. Step 6 (inspection) performs varioustests for the semiconductor device made in Step 5, such as a validitytest and a durability test. Through these steps, a semiconductor deviceis finished and shipped (Step 7).

FIG. 13 is a detailed flowchart of the wafer process in Step 4. Step 11(oxidation) oxidizes the wafer's surface. Step 12 (CVD) forms aninsulating film on the wafer's surface. Step 13 (electrode formation)forms electrodes on the wafer by vapor disposition and the like. Step 14(ion implantation) implants ions into the wafer. Step 15 (resistprocess) applies a photosensitive material onto the wafer. Step 16(exposure) uses the exposure apparatus 200 to expose a circuit patternon the reticle onto the wafer. Step 17 (development) develops theexposed wafer. Step 18 (etching) etches parts other than a developedresist image. Step 19 (resist stripping) removes disused resist afteretching. These steps are repeated, and multilayer circuit patterns areformed on the wafer. The device fabrication method of this embodimentmay manufacture higher quality devices than a conventional one. Thus,the device fabrication method that uses the exposure apparatus 1 anddevices such as resultant products constitute one aspect of the presentinvention.

Further, the present invention is not limited to these preferredembodiments, and various variations and modifications may be madewithout departing from the scope of the present invention. For example,the inventive exposure apparatus can use an optical pipe for the opticalintegrator, and a fly-eye mirror that includes reflective opticalelements for the optical integrator.

The present invention can provide an exposure apparatus that preventsshielding of the illumination light and has excellent imagingperformance.

In addition, the present invention can provide an exposure apparatusthat minimizes changes in performance (such as efficiency) other thanthe telecentricity when the telecentricity of the illumination ray shape(or an effective light source shape) is corrected, and has excellentimaging performance.

1. An exposure apparatus comprising: an illumination optical system forilluminating a reticle using light from a light source; and a projectionoptical system for projecting a pattern of the reticle onto an object tobe exposed, wherein said illumination optical system includes: anoptical integrator for forming a secondary light source from the light;a zooming optical system for introducing the light to the opticalintegrator, and for adjusting a size of the secondary light source; anda condenser optical system that introduces the light from the opticalintegrator to the reticle, and has a plurality of optical elements,wherein the zooming optical system adjusts the size of the secondarylight source in accordance with an adjustment of an interval between theplurality of optical elements of the condenser optical system.
 2. Anexposure apparatus according to claim 1, wherein the adjustment of theinterval between the plurality of optical elements is used to adjusttelecentricity for the light to expose the object.
 3. An exposureapparatus according to claim 1, wherein the condenser optical systemmakes a focal length and a back principal point position of thecondenser optical system substantially constant, while making a frontprincipal point position of the condenser optical system variable.
 4. Adevice fabricating method comprising the steps of: exposing an objectusing an exposure apparatus according to claim 1; and developing theobject that has been exposed.